This invention relates to overbasing a calcium petroleum sulfonate. In another of its aspects this invention relates to the preparation of a lubricating oil additive. In still another of its aspects this invention relates to the production of calcium petroleum sulfonate having a high total base number (TBN) for use as an additive in lubricating oils, particularly crankcase oils for internal combustion engines to impart detergency and reduce sludge formation.
In one of its concepts this invention provides a process for overbasing a calcium petroleum sulfonate by manipulation of process steps, particularly the addition of carbon dioxide, to provide a product having a TBN in desirable range.
Among the materials that impart detergency to lubricating oils thereby being of assistance in keeping internal engine parts clean and reducing sludge formation in the oil are overbased calcium petroleum sulfonates. These sulfonates are known to be useful as additives for lubricating oils, particularly crankcase oils for internal combustion engines.
It is known that equivalent detergency characteristics can be obtained with a lower concentration of additive in a lubricating oil --the higher the alkaline reserve of an additive: the larger the quantity of acidic combustion products accumulated in the oil to which the additive is added that can be neutralized by the additive. The measurement of alkaline reserve is reported as total base number (TBN) which is the number of milligrams of potassium hydroxide equivalent to the amount of acid required to neutralize the alkaline constituents present in one gram of sample. An additive having a total base number higher than can be obtained from calcium petroleum sulfonate alone is commonly said to be "overbased" or, alternatively, is said to be "superbasic".
Petroleum sulfonic acid which is neutralized to form petroleum sulfonates normally includes appreciable amounts of various hydrocarbons not having the acid group capable of forming the sulfonate so that the resulting product is a mixture of hydrocarbons and petroleum sulfonates. When the sulfonic acid is neutralized with an excess of CaO or Ca(OH).sub.2 to form the sulfonate, the resulting product has a relatively small alkaline reserve. The addition of a large excess of neutralizing material normally does not materially increase the alkaline reserve since the excess material is removed, usually by filtration, prior to the use of the sulfonate in a lubricant. The previously known processes for overbasing calcium petroleum sulfonates have experienced difficulty in obtaining sufficiently high alkaline reserves, e.g., TBN of 300 mg KOH/gm or higher, to enable the formulator to use lower amounts of additive while maintaining equivalent detergency or to protect the engine adequately under conditions of high acid formation in the combustion process.
It has now been found that overbased calcium petroleum sulfonates can be produced by a continuous process using a series of at least four, preferably five, stirred reactors to provide product having an alkaline reserve measured as a TBN of 300 mg KOH/gm or higher. The process has been found to be most flexible in that, since 300 TBN can be continuously achieved in four reactors, one reactor of the optimum five-reactor system can be taken off stream for maintenance without shutting down the entire unit.
It is therefore an object of this invention to provide an overbased calcium petroleum sulfonate having high alkaline reserve. It is another object of this invention to provide lubricating additive containing overbased calcium petroleum sulfonate having high alkaline reserve. It is another object of the invention to provide a process for preparing an overbased calcium petroleum sulfonate having high alkaline reserve. It is still another object of this invention to provide a process for preparing a lubricating additive containing overbased calcium petroleum sulfonate having a high alkaline reserve.
Other aspects, concepts, and objects of this invention along with its several advantages will be apparent from a study of this disclosure and the appended claims.